diff --git a/src/rstd/collections/pair.rs b/src/rstd/collections/pair.rs
index 17ea4fb..74f5115 100644
--- a/src/rstd/collections/pair.rs
+++ b/src/rstd/collections/pair.rs
@@ -201,3 +201,7 @@ impl<A: InliningAtomic, B: AtomicModeParse> AtomicModeParse for (A, B) {
         StaticPairObject::<Self>::ma_extend_sp(atomic, tail)
     }
 }
+
+impl<A: ConstSizeAtomic, B: ConstSizeAtomic + AtomicModeParse> ConstSizeAtomic for (A, B) {
+    const SIZE: usize = A::SIZE + B::SIZE;
+}